Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are highly heritable neurodevelopmental disorders that frequently co-occur. Family studies have shown that relatives of individuals with ASD have an increased risk of receiving a diagnosis of ADHD (1-3) and that the magnitude of the risk is higher in relatives who are more genetically related (3). This implies that ADHD and ASD might be influenced by partially shared familial factors that are likely to be of genetic origin.
This hypothesis is corroborated by twin studies, which have consistently found moderate genetic correlations between continuous traits of ADHD and ASD in the general population (4-7). In addition, because ADHD and ASD are considered heterogeneous disorders, researchers have relied on twin studies to examine associations among ADHD and ASD subscales. These studies have found that in children there were stronger phenotypic and genetic correlations between all ADHD subscales and ASD subscales related to communication and social difficulties (5-6). However, in adults, there was a stronger association between all ADHD subscales and ASD subscale related to restricted and repetitive behaviors (7).
In this review, we are going to summarize the evidence from family and twin studies regarding the possible genetic overlap between ADHD and ASD. We will compare results from studies using data on clinical diagnoses and traits continuously measured in the population in childhood, adolescence, and adulthood. Furthermore, we will investigate how the magnitude of the correlations between ADHD and ASD subscales may differ by age.
References
1) Musser, ED, Hawkey E, Kachan-Liu SS, Lees P, Roullet JB, Goddard K, et al. (2014). Shared familial transmission of autism spectrum and attention-deficit/hyperactivity disorders. Journal of Child Psychology and Psychiatry 55, 819-27.
2) Jokiranta-Olkoniemi, E, Cheslack-Postava K, Sucksdorff D et al. (2016). RIsk of psychiatric and neurodevelopmental disorders among siblings of probands with autism spectrum disorders. JAMA psychiatry.
3) Ghirardi, L, Brikell I, Kuja-Halkola R, Freitag CM, Franke B, Asherson P, et al. (2017). The familial co-aggregation of ASD and ADHD: a register-based cohort study. Molecular Psychiatry.
4) Ronald, A, Simonoff E, Kuntsi J, Asherson P & Plomin R (2008). Evidence for overlapping genetic influences on autistic and ADHD behaviours in a community twin sample. Journal of Child Psychology and Psychiatry 49, 535-42.
5) Taylor, MJ, Charman T & Ronald A (2015). Where are the strongest associations between autistic traits and traits of ADHD? evidence from a community-based twin study. European Child and Adolescent Psychiatry 24,1129–38.
6)Pinto, R, Rijsdijk F, Ronald A, Asherson P & Kuntsi J (2016). The Genetic Overlap of Attention-Deficit/Hyperactivity Disorder and Autistic-like Traits: an Investigation of Individual Symptom Scales and Cognitive markers. Journal of Abnormal Child Psychology 44, 335-45.
7) Polderman, TJ, Hoekstra RA, Posthuma D & Larsson H (2014). The co-occurrence of autistic and ADHD dimensions in adults: an etiological study in 17,770 twins. Translational Psychiatry 4, e435.
Developmental Disorders (e.g. ADHD)
